The emerging field of tissue engineering (TE) is poised to make enormous progress in the treatment of organ disease and dysfunction in the coming decade. In 2001, there were 23 cell-based therapeutics approved for market in the United States (U.S.) and Europe, of which nine were skin substitutes or grafts, and 100 more products were in development. (De Bree, Genomics-based Drug Data Report and Regenerative Therapy (1) 2:77-96 (2001)). In 2007, nearly 100 companies were involved in developing engineered tissues, cell-based therapeutics, or related technologies (Applied Data Research, February 2007). Overall the industry had an annual growth rate of 16% from 1995-2001. The “structural” industry segment (e.g., skin, bone, cartilage) showed 85% growth from 1998-2001. In 2004, the U.S. market for tissue-engineered skin replacements/substitutes and active wound repair modulators was valued at approximately $195 million. Sales are expected to increase at a compound annual rate of 9.5%, reaching approximately $481 million in the year 2014 (MedTech Insight, Windhover Information, September 2005). The total U.S. market for advanced wound care technologies was worth more than $2.3 billion in 2005. This has been projected to grow at an average annual growth rate of 12.3% over a five year period to reach $4.6 billion in 2011 (BCC Research, PHM011E, January 2007). The global wound care market is estimated to be worth US$ 7.2 billion in 2006 and comprises two sectors, traditional and advanced (Espicom Business Intelligence, 2007). Traditional wound care products consist mainly of low technology gauze-based dressings such as woven and non-woven sponges, conforming bandages and non-adherent bandages. The advanced wound care segment (US$ 4.1 billion global) is the fastest growing area with double-digit growth of 10% per year (Espicom Business Intelligence, 2007).
Although a multitude of revolutionary and economically important applications for engineered tissues and organs exist in the human health arena, the full economic potential of the industry is far from realized. At present, only one of the publicly-held tissue engineering companies worldwide has shown a profit despite global investment in these technologies exceeding $3.5 billion. (Lysaght and Reyes, Tissue Engineering 7(5):485-93 (2001)).
A major impediment to the acceptance of engineered tissues by medical practitioners, healthcare providers, and second party payers is the lack of a means to effectively and efficiently preserve and store engineered tissues. The nature of living cells and tissue products makes them impractical for long-term storage. Current engineered tissues must often be stored and shipped under carefully controlled conditions to maintain viability and function. Typically, engineered tissue products take weeks or months to produce but must be used within hours or days after manufacture. As a result, TE companies must continually operate with their production facilities at top capacity and absorb the costs of unsold product which must be discarded. These inventory losses, on top of already costly manufacturing process, have forced prices to impractical levels. As one specific example, APLIGRAF requires about four weeks to manufacture, is usable for only ten days and must be maintained between 20 and 23° C. until used. As another example, EPICEL is transported by a nurse from Genzyme Biosurgery's production facility in Cambridge, Mass. to the point of use in a portable incubator and is used immediately upon arrival. Such constraints represent significant challenges to developing convenient and cost-effective products.
Cryopreservation has been explored as a solution to the storage problem, but it is known to induce tissue damage through ice formation, chilling injury, and osmotic imbalance. Besides APLIGRAF, the only other approved living skin equivalent, ORCEL, is currently in clinical trials as a frozen product but has the drawback that it must be maintained at temperatures below −100° C. prior to use. This requires specialized product delivery and storage conditions, including the use of dangerous goods during transport, and use of liquid nitrogen for storage, which is expensive, dangerous, and not readily available in rural clinics and field hospitals. Moreover, delivering a frozen product requires special training on the part of the end user to successfully thaw the tissue prior to use.
Accordingly, what is needed in the art are improved methods of preparing engineered tissues and cells for storage under conditions that are routinely available at the point of use. As all clinical facilities have refrigerated storage, development of a skin equivalent that can be stored for prolonged periods in a standard refrigerator would greatly improve the availability and clinical utility of these products. Development of a skin equivalent that can be stored for prolonged periods at ambient temperatures would further increase the availability of such products for immediate use on the battlefield or in a variety of first response situations.